Npower came under fire in February from the UK government and the energy regulator after announcing plans to hike gas and electricity prices by 9.8 per cent – a move that added £109 to annual dual fuel bills.

Focusing on Npower’s performance, Innogy said: “The restructuring programme initiated at the beginning of 2016 led to a reduction in the cost base in the first six months of 2017, but the competitive landscape there remains very tough in the retail business.

“Following customer losses in the first quarter, however, some 50,000 new customers were acquired during the second quarter.

“Improved service performance also came to bear here: there was a marked reduction in the number of customer complaints.

“Of the big six energy companies in the United Kingdom, Innogy’s retail brand Npower had the second-lowest rate of customer complaints, whereas it received the highest number of complaints in 2015.”

Innogy said the number of UK electricity customers fell by 3 per cent to 2.82 million in the six months to June, while UK gas customers slipped by 2 per cent to 1.93 million.

Energy watchdog Ofgem said last month that it was considering introducing a price cap on bills as part of new proposals aimed at protecting vulnerable consumers.

A “safeguard tariff”, which would protect such customers from overpaying for their energy, is one of a number of options mooted.

The Conservatives promised a wider energy price cap that would benefit 17 million customers before the general election, but the policy did not appear in the Queen’s Speech following Prime Minister Theresa May’s failure to win a majority.